This invention relates to a solid state image device which has a vertical charge transfer portion and a parallel charge transfer portion, and in particular, to a connection portion therebetween.
A solid state image device of the type described has been recently used in an image device, such as a video camera and an electrical camera. In this device, an inputted optical signal is converted into an electrical charge signal. The converted electrical charge signal is transferred to an output portion via charge transfer portions.
More specifically, the above conventional solid state image device mainly includes a plurality of vertical charge transfer portions, a plurality of photo-electrical conversion portions, and a parallel charge transfer portion, as disclosed in Japanese Unexamined Patent Publications Nos. Hei. 8-260657 and Hei. 8-88344.
Herein, the photoelectrical conversion portions are arranged adjacent to each of the vertical charge transfer portions. Further, the parallel charge transfer portion is electrically connected to the vertical charge conversion portion at least one end side. Moreover, the parallel charge transfer portion is connected to an output circuit portion.
With such a structure, a plurality of charge transfer electrodes are arranged at each of the vertical charge transfer portions. In this event, the vertical charge transfer portions are connected to the parallel charge transfer portion via a final charge transfer electrode at the one end side.
With this structure, each length of the charge transfer electrodes is generally identical to each other to keep charge transfer efficiency and charge transfer capacitance in the conventional solid state image device.
In consequence, when a charge transfer duration from the vertical charge transfer portion to the parallel charge transfer portion is short, or when a charge transfer rate from the vertical charge transfer portion to the parallel charge transfer portion is slow, an output signal difference often takes place between the adjacent vertical lines. This is because a signal charge which is left in the connection portion between the vertical charge transfer portion and the parallel charge transfer portion is transferred into the parallel charge transfer portion at the subsequent timing at which the parallel charge transfer portion starts to transfer the charge. In particular, when the output signal is low, an abnormality with respect to a vertical line shape, which is generally called a black line defect, often brings about.
Further, under the above-mentioned condition, a part of the signal charge is inevitably left in the vertical charge transfer portion. In particular, when the output signal is low, the charge transfer efficiency is remarkably degraded.
It is therefore an object of this invention to provide a solid state image device which is capable of reducing remaining signal charge at a connection portion between a vertical charge transfer portion and a parallel charge transfer portion.
It is another object of this invention to provide a solid state image device which is capable of suppressing a black line defect and preventing deterioration of charge transfer efficiency.
A solid state image device according to this invention, a group of optical-electrical conversion portions are arranged in a vertical direction. In this event, each of the optical-electrical conversion portions converts an optical signal into an electrical charge signal.
Further, at least one vertical charge transfer portion is arranged adjacent to the optical-electrical conversion portions and transfer the electrical charge signal in the vertical direction.
Moreover, at least one parallel charges transfer portion is connected to the vertical charge transfer portion at one end and transfer the electrical charge signal in a parallel direction.
On this condition, a plurality of charge transfer electrodes constitute the vertical charge transfer portion. In this event, the charge transfer electrodes include a final charge transfer electrode coupled to said parallel charge transfer portion at the one end.
With such a structure, a first electrode length of the final charge transfer electrode is shorter than the other electrode lengths of the remaining charge transfer electrodes.
Consequently, the charge transfer distance from the vertical charge transfer portion to the parallel charge transfer portion becomes shorter than that in the conventional solid state image device.
Further, the charge transfer rate from the vertical charge transfer portion to the parallel charge transfer portion can be made quicker as compared to the conventional solid state image device because the fringe electrical field, which is the exponential function of the charge transfer distance, can be increased.
In consequence, no signal charge is left at the connection portion between the vertical charge transfer portion and the parallel charge transfer portion.
Moreover, even when the output signal is relatively low, the abnormality, such as the black line defect, can be effectively suppressed.